Hydrogel membranes were prepared by radiation crosslinking of poly (vinyl alcohol) (PVA) in aqueous solutions. Effects of PVA concentration, PVA molecular weight, and radiation dose on the permeation of insulin and immunoglobulin through the membranes were investigated. Glucose permeation was also studied. The crosslinking density affected the size of macromolecular mesh of hydrogel network as well as the water content of membrane responsible for the diffusion of the solutes. The diffusion coefficient linearly increased for all the solutes with the increasing water content in PVA hydrogels, indicating that diffusion occurs primarily through the water hydrating the polymer network. The increase in crosslinking density of hydrogels by changing PVA molecular weight brought about the decrease in mesh size of the hydrogels, which, in turn, had an influence on the diffusion of immunoglobulin, but not of insulin and glucose.
The resting spores of Olpidium brassicae in young root tissues of tobacco plants, observed in time sequence with a scanning electron microscope after freeze-fracturing, were first smooth spheres later developing ridges with pentamer and hexamer facets on the surface. Transmission electron microscope studies showed that the wall of mature resting spores consisted of three layers: inner, intermediate and outer. The cytoplasm was dense and contained many lipid-like bodies at the periphery. As individual zoospores developed fully, an exit tube containing membrane-bound vesicles was formed by the protrusion of the inner layer through the intermediate and outer layers of the wall. The result of computer image analysis supported these observations.